As the demand for hydrocarbon-based fuels has increased, the need for improved processes for separating hydrocarbon feedstocks of heavier molecular weight has increased as well as the need for increasing the conversion of the heavy portions of these feedstocks into more valuable, lighter fuel products. These heavier, “challenged” feedstocks include, but are not limited to, low API gravity, high viscosity crudes from such areas of the world as the Middle East, Mexico, Venezuela, and Russia, as well as less conventional refinery feedstocks derived from such sources as bitumen, shale oil and tar sands. It is also important that heavy crude fractions, such as atmospheric resids, vacuum resids, and other similar intermediate feedstreams containing boiling point materials above about 950° F. are processed in such a manner so as to improve their ability to be utilized as feedstreams for subsequent refining and petrochemical processes such as, but not limited to, fuels blending, fuels upgrading, catalytic conversion, steam cracking, and lube oils production and upgrading.
Most crude oils and synthetic crude oils derived from such raw materials as bitumen, shale oil and tar sands are processed through initial separations units such as a crude unit that are designed to boil and distill lighter boiling point fractions from the heavier boiling point crude fractions. The majority of these boiling point fractions are sent to other refinery and petrochemical processes for further refinement depending upon their molecular content characteristics, while a smaller amount of these crude unit fractions are sent to finished product treatment and/or product blending.
One problem that exists is that these conventional separations units require a significant amount of energy to generate these distillation based separations. Most crude units have at least one atmospheric distillation train and at least one vacuum distillation train. Often crude units also have additional crude intermediate or auxiliary distillation trains. Each of these unit trains require the hydrocarbon feed to the train to be heated to temperatures of about 750° F. to about 85° F. prior to entering a distillation column associated with each train. In turn, each of these distillation columns normally requires multiple reflux circuits and possible intermediate column reheat circuits in order to properly control and achieve proper separation of the individual fractions obtained from the distillation. Not only does this arrangement require a significant amount of equipment and associated capital and maintenance costs, but these conventional processes require large amounts of input energy as well as a large array of sophisticated controls and skilled personnel for proper operation.
In a typical refining unit, a significant portion of the bottoms product stream from the crude atmospheric distillation train is sent for further processing in a crude vacuum distillation train, This atmospheric bottoms stream is typically high in both asphaltene content and CCR content. The vacuum distillation train can separate out some of the asphaltene content and CCR via distillation at high temperatures under vacuum conditions, but this process is costly to operate. Additionally, as existing refineries are processing heavier crude feedstocks, Which are more available and lower cost than the currently dwindling lighter crude feedstocks, these existing vacuum distillation trains cannot process all of the atmospheric bottoms produced.
Efforts therefore have been initiated by refiners to find alternate processing methods for upgrading heavy oils, such as atmospheric bottoms streams, in order to divert some of the processing away from these overloaded vacuum distillation trains. As is expected, it is also desired if these alternate methods are lower in cost to operate than conventional distillation processes.
Filtration of heavy crudes, if made viable, is an attractive alternative to vacuum distillation due to the significant reduction in heat energy requirements (due to not requiring boiling of the hydrocarbon streams for distillation) as well as the elimination of performing operations under a vacuum as required by current distillation technologies.
The problem in the current art is to develop low energy filtration systems for producing lower CCR content crude products that have high enough filtrate (or “permeate”) flow capacities while maintaining significant CCR removal efficiencies to rival the economics of conventional thermal distillation techniques, thus making such filtration processes economically viable alternatives.